1. Technical Field
The present invention relates to a tuning fork type piezoelectric resonator element and a tuning fork type piezoelectric resonator.
2. Related Art
It is known that leak of vibration from resonator arms 902 is reduced if a base 904 having the resonator arms 902 extended therefrom is provided with cuts 906, with reference to FIG. 9 (see JP-A-2002-261575). However, the cuts 906 alone are not sufficient to stabilize the characteristics of a tuning fork type resonator element. For example, referring to FIG. 9, the vibration of the right and left resonator arms 902 may become irregular. In particular, if the tuning fork type piezoelectric resonator element is connected using a connecting member having an apparent elastic modulus, a dynamic storage elastic modulus, or a Young modulus during operation of 100 MPa or more, the frequency characteristics notably deteriorate and the resonator element does not stand practical use. The inventor of the invention analyzes that this is due to vibration of an X common mode. The X common mode vibration is, with reference to FIG. 10, vibration of the right and left resonator arms 902 in the same direction (in an X-axis direction when defining orientation of quartz crystal). Because a node of the X common mode vibration of the related-art tuning fork type resonator element is located around a section for connecting the resonator arms 902 to the base 904, the X common mode vibration has an inherent resonance frequency close to that of a required fundamental mode. As a result, the vibrations of the X common mode and the fundamental mode are combined, leading to deterioration of the characteristics. The inherent resonance frequency that generates vibration of the fundamental mode is higher than the inherent resonance frequency that generates vibration of the X common mode. If the two frequencies are close together, however, the inventors' analysis reveals that the X common mode vibration occurs even when excited in the fundamental mode. The fundamental mode herein indicates a mode of vibration at which the pair of resonator arms repeat approaching and separating to/from each other, and most tuning fork type piezoelectric resonators output inherent resonance frequencies of this fundamental mode.